Minimizing the creation of solid wastes and economical disposal of solid wastes have become very important in drilling of oil and gas wells. Stiffer environmental regulation, "cradle to grave" liability for solid wastes, and increased landowner restrictions have contributed to considerable increases in the cost of disposal of solid wastes. Generally, solid wastes such as drilling cuttings have been disposed of by burial, solidification, landfarming, annular injection and commercial disposal. Each of these methods have drawbacks.
Commercial disposal of drilling waste is very expensive, and can be only a temporary disposition for solid wastes because the originator can be found liable for remediation of disposal sites at a later time.
Burial, solidification and landfarming typically require that drilling fluids be removed from the solids. Removal of drilling fluids from drilling cuttings is particularly important when an oil-based or emulsion drilling fluids are used due to the contamination by the oil-based materials. Removal of the drilling fluids in turn results in generation of other forms of wastes.
Solidification of wastes is disclosed in U.S. Pat. Nos. 4,880,468 and 4,338,134. Patent '468 discloses combining hygroscopic material and a cementitious binder to material with drilling wastes to solidify drilling wastes. The cementitious binder is a Portland cement. Patent '134 discloses fixation of wastes with hydraulic mortar to enable easier disposal of the wastes. Injection of drilling wastes into an injection well is disclosed in U.S. Pat. No. 4,942,929. Large drilling cuttings are recovered, washed and used as construction gravel and smaller solids are separated from drilling fluids and pumped into a formation through the injection well.
Solidification also typically requires removal of residual drilling fluids from drilling cuttings because drilling fluids and cements are usually incompatible. Even most water based drilling muds will either cause instant setting of the cement or act as a retarder of the cement setting. Strength of the set cement is also adversely affected by the presence of most drilling fluids.
Solidification of the drilling solids within cement can fix contaminates and greatly reduce the expense of disposal, but solidification within cements has not been widely practiced due to the expense of cementing materials and the expense of removing incompatible drilling fluids.
U.S. Pat. Nos. 3,168,139 and 3,499,491 disclose the conversion of drilling fluids to wellbore cement slurries. Conversion of drilling fluids to cement slurries eliminates the need to dispose of used muds and eliminates the need to provided some additives, such as fluid loss and free water control additives that are already present in the drilling fluids. U.S. Pat. No. 5,058,679 discloses a process to convert drilling fluids to a wellbore cement slurry by adding blast furnace slag to acceptable drilling fluids. The use of the blast furnace slag as a cement compound significantly reduces the cost of converting the drilling fluids to cement compared to the use of Portland cements as cement compound. The use of blast furnace slag instead of Portland cement also provides for a slurry that is very compatible with the original drilling fluid resulting in other significant advantages.
It is therefore an object of the present invention to provide a method to dispose of drilling cuttings by solidification wherein removal of drilling fluids from the drilling cuttings prior to solidification is not necessary. It is an additional object to provide a method to solidify drilling cuttings wherein the cementation compound is blast furnace slag.